Trail bikes are generally better suited to more travel and 27.5. I would stay away from 26ers. They are becoming harder to find spares for. Marathon bikes, IMHO, are fine with 100mm travel, but definitely favour 29 and full-sus. Some hardcore guys prefer hard tails for marathons but that takes it out of you a little more, very bumpy and uncomfortable if you are in the saddle for 3 days. Those events you mention are definitely marathon events. I would go 29er full suspension. There are great bikes out there that cover this category. The "big name" bike that many favour is the Specialized Epic, which is a marathon thoroughbred. I am biased as I have one. As a good balance between trail and marathon, the Specialized Camber is awesome. Other great brands include the Momsen Vipa as a marathon/trail mix, Santa Cruz tall boy, and the Yeti ARc. These are all expensive bikes. Cannondale Scalpals are also highly recommended, but again, expensive. Slightly less expensive are the Giant Anthems and Merida Big Nines. I am sure that others have good recommendations as well, but those are the main ones that jump to mind for the cycling you are focusing on. You can test ride many of them. Take the opportunity to see which one in your budget you prefer. Last piece of advice... spend as much as you are comfortable with. Penny-wise, pound-foolish will only mean that you will want to upgrade to the better bike in +- 2 years time.
